N: Normal mode. Pulse rate and pulse width are adjustable. It generates continuous stimulation based on the setting value.
M: Modulation mode. The pulse rate is automatically varied in a cyclic pattern over an interval of nominally 10 seconds. (in max 150 Hz). Pulse rate decreases linearly over a period of 4 seconds from the control setting value to a value which is 40% less. The lower pulse rate will continue for 1 second, then increase linearly over a 4 second period to its original value. The original pulse rate will continue for 1 second. The cycle is then repeated.